Ability to remove all checked items

Hi,

One of my main usage of checkboxes in a document is for a shopping list.
The editor easily allows to add a new item, but every item has to be manually removed once we don't need them anymore.

In my case, whether it is a shopping or todo list, I need to remove every check item once in a while (after shopping for example).
I don't want to just put them at the end because most of the time the items change.

Describe the solution you'd like

I'd like an action, maybe in the 3 dots menu, or through a / command, to delete every checked item.

Describe alternatives you've considered

I opened a PR on the Nextcloud Notes for Android, but that only relates to direct notes, not the notes that are loaded through the webview and using Nextcloud Text. Nextcloud text also enables better edition conflicts, which is a must for me as I share my shopping list with my girlfiend.

Additional context

I can probably help implement this, but please tell how I should do it:

• Is there some kind of plugins interface on which I could add a new action?
• Is the 3 dots menu the best place to add such an action? Or the / command?
• Are there particular points I should be aware before starting to code this?

Start with the editor's existing three-dots menu, slash-command, and plugin interfaces mentioned in the issue; determine which entry point can expose an action for checked items. Compare it with the current checkbox editing behavior, with completion meaning that all checked items are removed while unchecked items remain unchanged.